Platy pigments are composed of a plurality of laminar platelets coated with one or more reflecting/transmitting layers. Typically, effect pigments are a laminar platy substrate such as natural mica or glass flake that has been coated with a metal oxide layer. A description of effect pigments' properties can be found in the Pigment Handbook, Volume I, Second Edition, pp. 829-858, John Wiley & Sons, NY 1988, which is incorporated herein by reference. If colorless metal oxides are used to coat the laminar platy substrate, effect pigments exhibit pearl-like luster as a result of reflection and refraction of light, and depending on the thickness of the metal oxide layer, they can also exhibit interference color effects. If colored metal oxides are used, the observed effects depend on reflection, refraction and absorption.
Platy pigments, such as effect pigments (also known as pearlescent pigments or nacreous pigments), are used to impart a pearlescent luster, metallic luster and/or multi-color effect approaching iridescence, to a material. It is, for instance, common to include platy pigments in cosmetic and personal care compositions, to contribute to or provide color, luster and/or pleasing tactile properties. Natural mica and metal oxide-coated natural mica have a surface hydrophilicity character that may not be suitable for interaction with skin. In addition, the hydrophilicity can affect the distribution or dispersion of the pigment in a cosmetic composition.
Surface modification of natural mica or metal oxide-coated natural mica with hydrophobic materials is known. See, for instance, U.S. Pat. Nos. 4,640,943; 5,326,392; and 6,780,826; and U.S. Pat. App. Pub. 2004/0223929.
There is an on-going need in the art for platy substrates and platy pigments with improved properties.